View Full Version : Slightly undersized AK-47 barrel
May 19, 2012, 11:37 AM
I have two AK-47 barrels that are about .008" too small to make a press fit to the front trunions. I am planing on using a knurling tool on my lathe to slightly expand the barrel to fit the trunion.
:rolleyes:Are there other options?
May 21, 2012, 07:08 AM
The problem with knurling, in general, is that the metal displaced by the process will migrate back under load. Since the breech end of a barrel is subjected to some pretty strong shock and whip, I'd not expect it to be a good idea.
May 21, 2012, 11:47 AM
Second the above... the knurled metal is not "added metal". It's displaced from someplace else. For every bearing surface "added" by knurling, another is removed... so the end result would be radial bearing surfaces but not on 100% of the designed bearing surface. There's always going to be a little air in there, so to speak.
With that said... similar technique has worked out OK in other applications. This is a fairly critical one though. Normally I would suggest "weld a ring and machine to diameter" but with heat treatment and all... not in this case. With that said, if you have someone who is very good with a TIG torch you might have them put 4 small dots of weld at 90 degree points at the most forward and most rearward areas where it matches the trunion, and then lathe-cut to a very slightly oversize dimension, and then press to fit. They need to "just" make the spots... with perfect control and lowest possible heat.
You "might" consider trying one with knurling backed up with judicious application of a high temperature epoxy as you make the press fit. My guess is that it would be OK for a very long while... but only a test will tell for sure.
Personally, I would try the knurl and epoxy, not a lot to lose in any event.
Have you thought about cross-pinning in addition to knurling and press fitting? Mark a hole on on the trunion so as to have a 3/32-1/8 or so cross pin be placed so that half of it's diameter will be in the barrel (IE: just a notch in the BBL will result), press fit, drill the hole, pin, and grind flush? That'll never move. Larger diameter pins will be easier to mark for and place.
Just a few ideas from an old hobby-smith.
May 21, 2012, 12:04 PM
Since this is an AK-47, it IS backed up by a barrel pin that is also press fit and sits in a groove in the barrel to keep it from moving in the Trunnion.
May 21, 2012, 12:21 PM
Rog-All... I've not played with rebarreling AK's, so was unsure. The basics of fit and press are the same as what I've done elsewhere, so looks like it's the right track. With that cross pin I'd be comfortable with the knurl and epoxy method with high confidence.
May 22, 2012, 07:29 AM
What kind of accuracy is possible from a barrel that lacks a solid fit into the receiver?
I'd guess that the answer is not promising, even by AK standards.
May 22, 2012, 08:47 AM
Accuracy with a weapon that spits out 75 @ 7.62 x 39 rounds in less than 60 seconds at a man 50 feet away, is NOT an issue.
Never heard of using an AK-47 for competition target shooting.
May 22, 2012, 08:58 AM
LocTite makes a grade of "plastic metal" for want of a better word, that the Miata group use's to repair crankshaft issue's. Their problem is the keyway wears when the vibriation damper becomes loose. The Loctite fix is what they use.
On the AK there is no vibriation like a engine running at 7000rpm. So that fix should work for you.
May 22, 2012, 09:30 AM
That sounds like a good solution. That would be better than JB Weld that might make removing the barrel later a problem.
I see by your user name you are a Jag person. I have a 1970 XKE, 1982 XJ6, and a replica 1936 SS-100
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